Method of treating vacuum tubes



April 27, 1926. 1,582,720

V, K. ZWORYKIN METHOD OF TREATING VACUUM TUBES Filed Feb. 16, 1922 WITNESSES: INVENTOR Wad/7771f /f. Z wary/rm I Patented Apr. 27, 1926.

UNITED S ATES i,i52,720 PATENT orrica,

VLADIMIR K. ZWOR'YKIN, OF KANSAS CITY MISSOURI, ASSIGNOR '10 WESTING- HOUSE ELECTRIC do MANUFACTURING COMPANY, A CORPORATION OF PENNSYL- VAN IA.

METHOD OF TREATING VACUUM TUBES.

Application filed February 16, 1922. Serial No. 536,915.

heat, as, for example, 1000 C. and the fila- To all whom it may concept:

Be it known that VLADIMIR; K. ZWORYKIN, acitizen of Russia, and a resident of Kansas City, in the county of Jackson and State of Missouri, have invented a new and useful Improvement in Methods of Treating Vacuum Tubes, of which the following 1s a specification.

My invention relates to vacuum-tube devices and particularly to methods of degasifying such devices.

Broadly speaking, the principal object oi? my invention is to provide a method oi treating vacuum tubes which, among other things hereinafter brought forth, admits of material economies in the time necessary for degasifyin the tube, which considerably decreases t e expense of such processes and which provides an improved vacuum tube having highly desirable operating characteristics.

In the usual process of treating tubes by bombardment in order to drive out the occluded gases from the elements containedtherein, the hardening process proceeds rapidly during the first few seconds, but almost completely stops after from two to .four minutes. This slowing up-of the hardening or evacuation is known as the fatigue elfect.

I have found, however, that, by periodically alternating the electrical conditions within the tube, the so-called fatigue effect may be materially decreased. and considerably greater vacuums obtained in shorter periods of time than has heretofore been possible. The fatigue effect may be avoided or practically eliminated in my invention, by employing a revolving commutator which reverses the polarity of the grid potential every few seconds. It hasalso been found that, instead of the commutator, it is possible to apply alternating potentials of commercial frequency to the controlling element of the tube.

I have further observed that the electrical characteristics of vacuum tubes, especially the plate impedances thereof, are influenced, to a large extent, by the treatment of the tube durmg exhaust. In vacuum tubes having coated filaments, it has been observed that, if the initial ener 'zation of the filament occurs with the p ate cold, the plate impedance of the tube is relatively high, but thatif the plate is first heated to a bright ment then energized, the plate impedance is c0ns1derably reduced.

I have still further found that an apprecrable quantity of gas is released at the point of t1pping during the sealing operat1on of the tube and that, if the tipping or sealing operation is so arrested, when the connection of the evacuating means is almost closed, as to admit of such gases being removed and the final sealing of the tube then completed, a tube of exceptional hardness is obtained. With these and other objects in View, my invention consists in the mode of operation and the constructional details hereinafter described and claimed and illustrated in the accompanying drawing, wherein:

The single figure is a diagram-mafia view of circuits and apparatus embodying my in vent1on; v 1

In the drawing is shown a vacuum-tube device 1 of well known design comprising a containing envelope 2 and an anode 3, a grid electrode 4: and a hot cathode 5 suitably dis osed therein and provided with external circuit terminals 6, 7 and 8, 9, re spectlvely. A main exhaust tube 11, preferably 0 glass, is sealed to a vacuum pump (not shown) and to the containing envelope 2.

The elements contained within the envelope 2 may be'heated to any desired temperature by means of a high-frequency magnetic field produced by a magnetizing wind ing 12 which is suitably disposed thereabout. Terminals 13 and Li of the high-frequency winding 12 may be connected to any available source of high-frequency currents, such, for example, as a vacuum-tube oscillator (not shown). The filament or hot cathode 5 may be energized by connecting the filament terminals 8 and 9 to a source of energy 15 through a resistor. 16 and a switch 17. While a direct-current source of energy 15 is shown for energizing the filament 5, it is apparent that an alternating-current source is connected across the circuit terminals 6 and 8' through a switch 23. The dlrectcurrent generator 22 may be replaced, if-

in the exhaust-treatment process have been found to give satisfactory results for the articular type of tube experimented upon, ut, of course, my invention is not necessarily limited to such values.

When the envelope 2 has been scaled to the evacuating system, represented by the tube 11, the vacuum pump (not shown) is started and is maintained in operation continuously throughout the process. When the air has been substantially removed, the tube is given a preliminary baking, as, for example, for fifteen minutes at approximately &00 C. in a well known type of oven (not shown). The effect of the preliminary baking is to remove the water vapor from the elements contained in the tube before they are subjected to higher temperatures.

The magnetizing winding 12 or so-called induction furnace is now energized sufficiently to cause the anode 3 to be heated to a red heat, at temperatures ranging between 900 and 1200 C. When the anode has become red hot, the switch 17 is closed to energize the filament 5 to its normal operating temperature, requlrin say, 0.28 am eres, and the switch 23 is c osed, whereby directcurrent ener of saturation value, say, 110 volts, is applied to the anode 3. At the same time, the switch 21 is closed and a low-frequency alternating potential of approxi mately 20 volts is impressed upon the grid 4, thereby variably impeding the electron stream between the cathode 5 and the anode 3.

The effect of the resulting electron bombardment of the anode 3 is to materially increase its temperature. The several elements enclosed within the envelope 2 are further heated by the inductive efl'ects of the high-frequency winding 12. The induction furnace is maintained in operation until the plate current becomes steady, which may require, say, fifteen seconds, dependingupon the size of the elements, during which time the gases are entirely removed from the elements contained within the envelope 2.

The tip 24 of the envelope 2 is then drawn down to approximately of an inch, or until it is almost, but not quite, closed. Power is then again supplied to the induction furnace, say for thirty seconds, whereby the degasifying process is continued in order to remove the gases given ofi at the tip during the sealing operation. The several energy sources are then disconnected from the tube and the tip 24 is rapidly sealed off.

In ractice, I have found that by iin ressing a ternating otentials on the gri 4, I am able to pro uce vacuum tubes of sufiicient hardness after thirty seconds treatment in the high-frequency ma netic field, whereas, by the ordinary bom bardment method,

employing a non-reversing grid polarity,

the time required for obtaining a much' plate impedance by more than 65%, as compared with the results otherwise obtained.

Still another important feature of my process is the interruption of the sealing operation, when the connection with the envelope is almost closed, in order to remove the gases liberated by the sealing operation itself, thereby providing a vacuum tube having a higher degree of hardness than has heretofore been possible to obtain. Other advantages of my invention will readily suggest themselves to those skilled in the art.

While I have shown and described only one embodiment of my invention, for the purpose of illustrating its underlying principles and applications, it is apparent that various changes and modifications may be made therein without departing from the spirit of my invention and I desire, therefore, that only such. limitations shall be imposed thereon as are specifically set forth in the appended claims or demanded by the prior art. I claim as my invention: l. The method of evacuating a thermionic device having an electron-emitting element, a plate element and a controlling element which consists in substantially reducing the gaseous pressure in said devlce, subjecting said plate element to a high-frequency magnetic field ofsuch intensity as to heat said plate to a red heat and subsequently energizing said electron-emitting element, causing an electron discharge between said electronemitting element and said plate element and applying a periodically reversing potential to said controlling element.

2. The method of evacuating a space-discharge device having an electron-emitting element, a plate element and a controlling element which consists in substantially reducing the gaseous pressure in said device, subjecting said plate element to a high-frequency magnetic field of such intensity as to heat said plate to a red heat and subseuently energizing said electron-emitting e ement causing an electron discharge be-.

tween said electron-emitting element and said plate and applying a periodically reversing potential to said controlling element while continuing to subject said elements to said high-frequency magnetic field, whereby the gases may be driven from said elements.

3. As an improvement in the art of exhausting an envelope, the method which consists in evacuatin said envelope, starting the sealing of sai envelope from the evac: uating means, arresting the sealing of the envelope for a brief interval of time when the connection with the evacuating means is almost closed while continuing the evacuation to remove the gases evolved in the sealing process and finally completely sealing said envelope while highly evacuated.

4. As an improvement in the art of exhausting an envelope containin an element, the method which consists in su jecting said element to high temperatures to expel the gases therefrom, in evacuating said envelope, in starting the sealing of the envelope, in arresting the sealing for a brief interval of time when the connection with the evacuating means is almost closed while maintaining the temperature of said element and the degree of evacuation to remove the gases evolved in the sealing process and fievacuating device, operating said evacuating device, heating said anode to substantially a red heat, subsequently producing an electron-bombardment from said cathode to said anode, causing the intensity of said bombardment to vary at frequent intervals substantially as described, whereby occluded gases are removed substantiall without the development of the fatigue e ect, drawing said tip down until it is almost but not quite, closed, again treating said tube to drive off occluded gases, removing said gases and completing the sealing of the tip.

In testimony whereof, I have hereunto subscribed my name this 7th day of February, 1922.

VLADIMIR K. ZWORYKIN. 

